BEIRUT: The United Nations reacted with shock Tuesday to a report that the Syrian regime had systematically tortured and killed thousands of prisoners in a manner one lawyer described as reminiscent of Auschwitz.

The report’s release, timed to coincide with the beginning of Geneva II peace conference Wednesday, piled pressure on those attending the talks to make meaningful headway confronting human rights abuses.

The 31-page report, written by a team of global experts and first leaked to the Guardian and CNN, is based on thousands of photographs smuggled out of Syria by a defector from Bashar Assad’s government. The former military policeman, identified in the report only as “Caesar,” photographed the corpses of tortured prisoners whose deaths were then attributed to “heart attacks” or “breathing problems.”

Three prominent international lawyers penned the report based on Caesar’s testimony and concluded that there was clear evidence of “systematic torture” of 11,000 prisoners between March 2011 and August 2013. These findings could support a prosecution of “crimes against humanity” and “war crimes,” the experts said.

The harrowing photographs show evidence of strangulation, electrocution and starvation. Some of the corpses appeared to have had their eyes gouged out.

Desmond de Silva, one the report’s authors, said the photographs evoked images of Nazi death camps during World War II.

“Some of the images we saw were absolutely reminiscent of pictures of people who came out of Belsen and Auschwitz,” the ex-chief prosecutor of the special court for Sierra Leone said. “It is the tip of the iceberg because this is 11,000 in just one area.”

“This is not to say that the people on the other side have been free of serious crime. I think there is evidence that has led very responsible people to say there have been crimes committed on both sides,” he added. “But this industrial killing of people in detention in our view is clearly that of the government.”

Rupert Colville, spokesman for U.N. rights chief Navi Pillay said the report was “extremely alarming, and the alleged scale of the deaths in detention, if verified, is truly horrifying.”

Washington echoed the U.N., with State Department spokeswoman Marie Harf describing the images as “extremely disturbing.”

Caesar told the investigators he photographed as many as 50 bodies a day. However, he did not claim to have witnessed any torture or executions firsthand, a fact that lawyers said gave weight to his testimony.

Assad’s government did not comment directly on the dossier, but had previously denied accusations of human rights abuses, regularly blaming “terrorists” for attacks on civilians.

The report’s release appears to have been timed to coincide with the beginning of a Syria peace conference, designed to find a negotiated solution to the 34-month conflict. The talks – dubbed Geneva II – are due to begin Wednesday, but have been plagued with challenges over who will attend and what role Assad will have in the future of Syria.

Qatar, which has been providing the rebels with weapons and has called for Assad’s removal from power, commissioned and funded the report.

Although evidence of torture by the regime and the rebels has been documented before, the breadth and detail of the crimes documented in the report makes it perhaps the largest dossier on the alleged crimes of the Syrian regime.

Human Rights Watch said that the report should add to growing international pressure to put humanitarian concerns at the top of the agenda in Switzerland.

Speaking to The Daily Star, HRW researcher Cilina Nasser said the photographs “highlight the urgent need for those involved with Geneva to put the human rights situation first.”

“Every family has somebody who is detained or subject to enforced disappearances. So if the key players at Geneva are able to seriously tackle human rights violations, it would be an opportunity to gain the trust of the Syrian people.”

She said the report was consistent with HRW’s own research into torture, but added that if allegations in the report are true then they represent crimes against humanity committed “on a staggering scale.”

However, despite the growing body of evidence, the prospect mounting an international criminal case for human rights violations during the conflict appears unlikely in the current diplomatic climate.

As Syria is not signed up to the International Criminal Court, a prosecution could only be brought following Syria’s referral by the U.N. Security Council.

Russia, a staunch backer of Damascus, has veto-wielding powers at the Security Council and is likely to use them to block any such referral.